This is my first attempt at an SCP and I would really appreciate some feedback, since I really have no idea how good or bad it is. I will write an addendum within the next week, probably about a breach but I'm not sure.

This doesn't make much sense with the way it's worded. If it's color changes, I'm certain they can identify what colors they are. Are they typical colors? Rainbow? I don't know, and shouldn't need to ask.

At about 12:05, SCP-0000 will collapse, It’s flesh rapidly decaying.

its, not it's, and unnecessary capitalization. It helps to hammer out most SPAG errors before coming to the forums for review. You don't want to distract critique form the important bits, after all.

At 12:08, when the flesh has decayed to be nothing but bone

A bit of a grammer issue here, as well as a tonal issue. Suggestion:

Over the course of approximately three minutes, SCP-000 will rapidly decompose, with only its osseous matter remaining.

SCP-0000-1

I don't think you need a separate designation here.

SCP-0000-1 gains aproximately [DATA EXPUNGED] points of IQ and a large amount of hostility when the transformation is complete, and can identify many human objects, including weapons and surveillance systems.

Multiple problems here. First off, approximately. Second, the expungement is entirely pointless. Third, 'large amount of hostility' is poor tone (How much is a large amount?). What does it mean that it can identify those things? Do they use flash cards? How can they determine its IQ points?

brute force

Is too colloquial, try: 'blunt trauma'

SCP-0000-1 must be contained while separated.

This goes without saying. Also, why not separate and store it? Seems like the most efficient way to handle this one.

Even once this is all ironed out, I'm not seeing much in the way of a narrative. This is a basic monster at the moment, and the idea will need to be developed further to make it viable. If I may ask, why does this thing exist, and work the way it does?